There is a proposal for an optical receiver that has plural light receiving devices installed inside a sealed container (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2011-175133).
In optical transmission, there is recently demand, in optical receivers that split a received beam and receive the light with plural light receiving devices, for a function to detect signal interruptions, and to monitor the intensity of optical phase modulated signals input as a parameter in demodulation. There is accordingly a demand to provide inside the housing of the optical receiver both light receiving devices that measure the input main signal beam, and a light receiving device that measures a monitoring beam. It is desirable in such cases to achieve a configuration enabling good positional alignment to be attained for the light receiving device that measures the monitoring beam.